Preparation of arylenethiazole vulcanization accelerators



Patented Aug. 18, 1953 PREPARATION OF ARYLENETHIAZOLE VULCANIZATION ACCELERATORS David J. Beaver, Richmond Heights, Mo., as-

signor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware 7 No Drawing.

Original application November 24,

1948, Serial No. 61,897. Divided and this application May 14, 1951, Serial No. 226,295

3 Claims. (Cl. 260-3065) This invention relates to the vulcanization of rubber and to the vulcanized rubber products obtained thereby. More particularly it relates to a new and novel group of vulcanization accelerators.

The rubber industry has long concluded that for most purposes no single accelerator is capable of producing satisfactory vulcanizates and as a result the research chemist and the rubber technologist have sought a combination of compounds, one or both capable of vulcanizing rubher, which will give satisfactory properties as to rate of cure, absence of scorch and desirable physical properties in the vulcanizates. A combination of compounds, particularly a combination of accelerators, offers a great range of compound variation such that a series of combinations varying in scorch and curing properties may be obtained.

It has been found in accordance with this invention that heating a free mercaptan of the structure C-SH where R is an arylene nucleus with a sulfur halide in the absence of a solvent, with elimination of hydrogen halide, produces stable complex products possessing accelerating properties. It is preferred to employ sulfur monohalides since much more potent accelerators are obtained than from sulfur dihalides. The preferred class of condensation products represent a class of economical, non-scorchy, readily compatible accelerators which per se produce low modulus vulcanizates and when employed in conjunction with basic secondary accelerators are strongly activated thereby producing vulcanizates of high modulus.

Compounds possessing the group are members of a well defined class of compounds comprising 2-mercapto arylene thiazoles and their alkyl, aralkyl, cycloalkyl, halogen, hydroxy, amino, and nitro arylene substituted analogues. As specific examples of compounds possessing the desired grouping are Z-mercaptobenzothiazole, 2 mercaptonaphthothiazole, 2- me'rcaptc--methyl benzothiazole, 2-mercapto- 4,6 dimethyl benzothiazole, 2 mercapto 4- chlorobenzothiazole, 2-mercapto-6-phenyl benzothiazole, and 2 mercapto 6 ethoxy benzothiazole.

The new accelerators are readily prepared by condensing a free mercapto arylene thiazole with a sulfur halide at a temperature preferably above the melting point of the particular mercapto arylene thiazole. While the condensation is preferably carried out by reacting the molten mercapto thiazole with the sulfur halide, lower temperatures may be used if desired providing hydrogen chloride is eliminated. As exemplary of the preparation of the new accelerators, the following example is illustrative and it is to be understood that it is not limitative thereof.

EXAMPLE 1 173.1 parts by weight (substantially 1.0 mol) of Z-mercaptobenzothiazole was placed in a 3-neck fiask equipped with a thermometer, a stirrer, and a reflux condenser. The reaction vessel was then immersed in an oil bath at C. To the molten mercaptobenzothiazole was added dropwise 75.0 parts by weight (substantially 0.5 mol) of sulfur monochloride with stirring over a one-half hour period. An evolution of hydrogen chloride accompanied the addition of the sulfur monochloride. The agitation continued for one-half hour, the evolution of hydrogen chloride ceasing. A dark yellow-brown syrup formed which was taken up in toluene, Washed with water and dilute caustic soda, and evaporated to dryness. 200.0 parts by weight of a yellow gum like material was obtained which was then recrystallized several times from hot methyl alcohol. A yellow crystalline material was isolated having a melting point of 119-121 C. and a, sulfur and nitrogen content respectively of substantially 50.0% and 6.8%.

The above prepared complex condensation product is not to be confused with the reaction product of Levi, Gazz. chim. ital., 61, pp 383-387, 1931, who describes the reaction of sulfur monochloride with the zinc salt of mercaptobenzothiazole in a cold atmosphere. Levi identified the reaction product as mercaptobenzothiazole Pale crepe rubber "parts by weight. 100 Zinc oxide 5 Sulfur 3 3 Stearic acid-., 1 i 1: Diphenyl guauidine d .i g Q2375" Mercaptobenzothiazole-S1O] z condensation pro duct of Example 1 i-. do,.-, V L 0.7!:

The rubber stocks so compounded were wee canized in the usual manner by heating in a Dress for different periods of time at 142 C. The physical properties of the cured rubber products are set forth below.

Tahit tMin. cure Iat 152 0,, A B

63 263 1 lb 3 I g0; 00 en .5" s 60 120 273 90 110 240 15- i 130 1,103 170 1,147 500% modulus lbs-Ji'nfl 250. 1,.250 60 317 1,087 90 300 953 15. 1, 940 3,853 30 2,123- 3,907 Ultimate tensile, 1bs./in. 45 2,280 3, 520 60 2,247 3397 90 2, 333- 3,350 15' 8 683 30.: 867 677. Ultimateelougation,percent 45, 810v 657. 60' 793 657' 90 797 677 From the dataset forthabove it is shown that the condensationproductof*sul'fur-monochloride; and inercaptobenzothiazole is an accelerator and-'- when employed conjunction with a guanidine accelerator exhibits fast-curing properties.

As further exemplary of the exceptional accelerator properties and the activation potential ofthenew accelerators the yellow gum: like mercaptobenzothiazole-sulfur chloride condensation product, above preparedjwa-s incorporated" in a typical treadstoclricomprising Stock l C D, E

Smoked sheets rubben -parts by Wei 100 100 Zinc oxide l 5 5 2 22 Blend of aceto e-amin product anddiphenyl. mine l; 5 ll 5. Diphenyl guani'dine l 0. 25' 0. 375. l\lercaptobenzothiazole-SzC1 tiontpro pLExampl 0: 0.: 75

Stock 4 Table 2 cure 300% modulus in lbs/in.

500% modulus in lbs/113. 3

Ultimate-tensile; inlbsz/irr.

wcw wv-wooamwvomu oaweo rooorocnoovicvroocnocno a m Ultimate elongation, percent It is obvious from the above tabulated data that. the. mercaptobenzothiazole-sulfur halide condensation products are a class of excellent non-scorch, low modulus producing vulcanization accelerators which are readily activated to produce vulcanizat-es of a range of high moduli and possessing a long range of cure.

Other basic nitrogen containing acceleratorsthan diphenyl guanidine may be employed in conjunction with the new accelerators, as for example, di-p-tolyl guan-idine; diX-y-lyl guanidine, triphenyl guanidine, and the like; The bi uanides andthe aldehyde-amine accelerators may" be incorporated alsoas coaccelerators or activatorsin a rubber stock to produce d sirable-I p'- erties both in stock processing and inthe'final' product.

Asfurther embodiments of the invention ill'us 4G trating accelerating properties insynthetic rub- G R-Smubber; parts by wcghtl.

d Mercaptobenzothiazole-SzOlz condensation prcducL .do.

Stock v 300% modulus -in.1bs./in. Ultimatetensile in'lbs:/ii1: Ultimate;clcngation; percent e-..

The amount otthe new accelerators employed will vary depending upon whether or not they are admixed withother accelerators, thetype-Of stock, the type of rubber, the temperature of cure, the time of cure, tlie particular accelerators involved, and the objectives off the compounder,

;. i. e. whether a low or high modulus is required.

Bythe-tern'r-rubber as employedin'the appended claims ismeant rubber" in ageneric sensewhich: includes, natural; asWell as synthetic rubbers; which; are,:.capable of vulcanization When. 5 heated-r with sulfur, and; includes: laticesand re claims of such materials whether or not admixed with pigments, fillers, softeners, antioxidants, etc.

By the term condensation as employed in h specification and in the appended claims is meant the union of two unlike molecules, accompanied by the elimination of a simple molecule, e. g. in the present case the simple molecule eliminated is hydrogen chloride.

While specific embodiments of the invention have been described in detail herein, it will be understood that the invention is not limited but that various modifications may be made therein without departing from the spirit or scope of the invention.

This is a division of co-pending application Serial No. 61,897, filed November 24, 1948, now abandoned.

What is claimed is:

1. Method of making an accelerator composition which comprises heating with elimination of hydrogen halide in the absence of a solvent above the melting point of the thiazole substantially two molecular proportions of a free mercaptoarylenethiazole and. substantially one molecular proportion of a sulfur mono halide and recovering a composite reaction product.

2. Method of making an accelerator composition which comprises heating with elimination of hydrogen halide in the absence of a solvent above the melting point of the thiazole substantially two molecular proportions of a mercaptobenzothiazole and substantially one molecular proportion of a sulfur mono halide and recovering a composite reaction product.

3. Method of making an accelerator composition which comprises heating with elimination of hydrogen chloride in the absence of a solvent above the melting point of the thiazole substantially two molecular proportions of Z-mercaptobenzothiazole and substantially one molecular proportion of sulfur monochloride and recovering a composite reaction product.

DAVID J. BEAVER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,661,998 Carson Mar. 6, 1928 FOREIGN PATENTS Number Country Date 382,940 Great Britain Oct. 31, 1932 

1. METHOD OF MAKING AN ACCELERATOR COMPOSTION WHICH COMPRISES HEATING WITH ELIMINATION OF HYDROGEN HALIDE IN THE ABSENCE OF A SOLVENT ABOVE THE MELTING POINT OF THE THIAZOLE SUBSTANTIALLY TWO MOLECULAR PROPORTIONS OF A FREE MERCAPTOARYLENETHIAZOLE AND SUBSTANTIALLY ONE MOLECULAR PROPORTION OF A SULFUR MONO HALIDE AND RECOVERING A COMPOSITE REACTION PRODUCT. 